Method of separating alkyl anilines



Patented May 16, 1933 UNITED STATES PATENT. QFFHIE EDGAR C. BRITTON ANDRAY D. HOLMES, OF MIDLANI), MICHIGAN, ASSIGNORS TO THE DOW CHEMICALCOMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN METHOD OFSEPARATING ALKYL ANILINES No Drawing.

As prepared by the usual methods, the dialkylated aniline derivatives,such as climethyl aniline, diethyl aniline, 'dimethyl ptoluidine.dimethyl p-phenylene diamine, etc.

contain also some mono-allrylated aniline derivative. Thesemono-alkylated derivatives although not detrimental in all usages inwhich the dialkyl anilines are employed in the arts, are, however,harmful in some cases,

1. and must be removed for such usage. For

instance, if mono-methyl aniline be present in dimethyl aniline to theextent of over 1%,

the preparation of nitroso dimethyl aniline therefrom is unsatisfactorydue to the presence in the product of N-nitroso methyl aniline; and suchraw material is unsuitable gor this purpose unless in some manner puri-Several methods have been proposed and 0 used for this purification, butnone capable of yielding a pure product without the use of expensivereagents or costly procedure. A process for the separation of dialkylaniline and mono-alkyl aniline. for purifying either,

2 is accordingly highly desirable.

To the accomplishment of the foregoing and related ends, the invention,then, consists of the features hereinafter fully described, andparticularly pointed out in the claims, the following descriptionsetting forth in detail certain procedure in the application of theinvention such being illustrative however, of but a few of the variousways in which the principle of the invention may be employed.

In accordance with our invention, the alkyl anilines to be separated areheated with phthalic anhydride. This reacts with monoalkyl aniline toform mono-N-alkyl-phthal- 40 anilic acid, as may be represented in thefol I lowing equatlon The resulting acid may be readily separated fromthe unreacted dialkyl aniline in vari- Application filed. September 23,1927. Serial No. 221,612.

ou's ways, as will be described more in detail. A small amount ofdi-N-alkyl-phthalanilide may also form, but this compound is easilyseparated from the dialkyl aniline by distillation. The followingequation represents the reaction for the di compound:

0 0 n. 2 NH.IR /o O (monoalkyl aniline) (phthalic anhydride)(di-N-alkylphtha1ani1ide) generally syrupy liquids which are difficultto obtain in pure form, becomingwaxy on cooling. Having a free carboxylgroup present, they can, however, be separated from the di-ethyl anilineby forming their alkali metal salts, the following equation illustratingthe reaction where caustic soda is thus used:

(sodium-N-alkyl-phthalanilate) Thesephthalanilate salts are soluble inwater and insoluble in the dialkyl anilines, and this characteristicaffords one method of separation. Thedialkyl anilines have, furi Thesemono-N-alkyl-phthalanilic acids are N-alkyl-phthalanilic acid. Thischaracteristic affords a second method of separating. Or, if it isdesired, the dialkyl aniline may be steam distilled from the phthalicacid derivative. In any of these procedures of separating the dialkylaniline from the phthalic acid derivative, a pure dialkyl aniline isproduced.

In addition to the above mentioned procedures which may be practiced,further treatment of the phthalic' acid derivative may be carried outfor the purpose of producing pure monoalkyl aniline, as well as forrecovering the phthalic anhydride. The N-alkyl-phthalanilic acids may behydrolyzed readily by aqueous acid, or alkali solutions using heat underpressure, producing the monoalkyl aniline which may be recovered pureand the phthalic acid which may be returned to the process for, reuse.The following equations of the reactions involved are:

First using alkali solution:

As illustrative examples showing possible proportions, the following maybe noted (l) 300 g. by weight of dimethyl aniline containing 1.2% ofmono-methyl aniline were heated for about four hours at a temperaturearound100 C. with 7 g. of phthalic anhydride. By direct distillationunder reduced pressure, 288 g. of dimethyl aniline having a F. P. of 224C. were recovered.

(2) Steam distill the residue from Example 1 until all di-methyl anilineis removed. Then add 25 cc. 50% sulphuric acid and heat to 100 C. Dilutewith 25 cc. water and filter off phthalic acid. Treat filtrate with 50cc. 30% caustic soda solution and steam distill out the mono-methylaniline.

' 800 g. of dimethyl aniline containing 1.2% of mono-methyl aniline wereheated for about four hours at a temperature of around 100 C. with .10g. of phthalic anhydride. After reaction, the dimethyl aniline waswashed with 44 cc. of 10% caustic soda solution, following which themass was allowed to (mono-alkyl-aniline) I OOOH ooon V (phthalic acidmono-alkylaniline hydro sulphate) OH COONa IV. 2NaOH C0NR.C0H5 COONa(mono-N-alkyl-phthalanilic acid) (Sod. phthalate) GOONa 7 COOH V. 21101-i NaCl COONa COOH (Sod. phthalate) (free phthalic acid) 1 0 00011 o VI.heat E 0 0 OOOH v C40 (phthalic acid) I (phthalic anhydride) Second,using acid solution COOH VII. H2804 H2O common. (N-alkyl-phthalanilicacid) 0 4 O O OH O I VIII. heat O H2O (mono-alkyl aniline hydrosulphate]These two methods of hydrolysis of the N-alkyl-phthalanilic acid may bepractised as seems advisable. The acid hydrolysis can be carried outwith quite dilute acid, or desirably with 50% sulphuric acid veryreadily at about 100 C. i c In all of the foregoing equations, it willbe understood that -R represents analkyl' group.

(mono-alkyl aniline) or layer was then steam distilled to drive offoccluded dimethyl aniline, giving 10 g. oil

'F. P. of 2C. after being dried over anhydrous sodium sulphate. Thisalkaline solution was then heated under pressure at around 180 C. forabout four hours and 3 g.

of mono-methyl aniline were obtained. Upon acidification 9 g. ofphthalic acid were recovered.

(4) 100 g. of diethyl aniline, freezing point of- 878 C. were heated at135 to 140 C. for four hours with 3.1 g. of phthalic anhydride. At theend of the period of heating onehalf of the reaction mixture wasdistilled direct, and gave a diethyl aniline having a freezing point of36 (3., the other half was washed with a 10% caustic soda solution andthen was distilled giving a diethyl aniline having a freezing point of35.6 C. I

From the foregoing description, it will be seen that the process isreadily adapted for separating di-alkyl aniline from mono-alkyl aniline,or vice versa, in order to make either the pure mono or di compound; i.e. the process may be regarded as one for purifying either such compoundby removing the other. The process is, moreover, inexpensive to carryout, and while easy to apply, it is nevertheless capable of producingthese mono and di-alkyl anilinesin a state of greater puritythanheretofore attained by any method of which we have knowledge.

Other acid anhydrides in addition to phthalic anhydride, for examplesuccinic anhydride, have the characteristic of reacting with amono-alkyl aniline to form an acid corresponding withmono-N-alkyl-phthalanilic acid, and so may be utilized in the mannerhereinbefore set forth for effecting the separation of such mono-alkylaniline from di-alkyl-aniline.

Other modes of applying the principle of the invention may be employed,change being made as regards the details disclosed, provided the stepsstated in any of the following claims, or the equivalent of such steps,be employed.

We therefore particularly point out and distinctly claim as ourinvention:

1. A process of separating N-monoalkyl and N-dialkyl aromatic amines ofthe benzene series from a mixture thereof which comprises reacting theN-monoalkyl aromatic amine with a dicarboxylic acid anhydride at atemperature below approximately 140 G, in the absence of a solvent, andseparating unreacted N-dialkyl amine from the reaction mixture. 7

2. A process of separating N-monoalkyl and N-dialkyl aromatic amines ofthe benzene series from a mixture thereof which comprises reacting theN-monoalkyl aromatic amine with a dicarboxylic acid anhydride at atemperature below approximately 140 (1., in the absence of a solvent,and distilling unreacted N-dialkyl amine from the reaction mixture.

3. A process of separating N-monoalkyl and N-dialkyl aromatic amines ofthe benzene series from a mixture thereof which comprises reacting theN-monoalkyl aromatic amine with a dicarboxylic acid anhydride at atemperature below approximately 140 0., 1n thelabsenceof a solvent,distilling unreacted N-dialkyl amine from the reaction mixture undersub-atmospheric pressure, hydroi lyzing the residue through heating thesame with aqueous caustic alkali, andseparating the N-monoalkyl aromaticamine from the hydrolysis" mixture. 4. A process of separatingN-monoalkyl and N-dialkyl anilines from a mixture thereof whichcomprises reacting the N -monoalkyl aniline with phthalic anhydride at atemperature below approximately 140 (1., in

the absence of a solvent, and separating 'unreacted N-dialkylaniline-from the reaction mixture. 7 x

5. A process of separating N-monoalkyl and N-dialkyl anilines from amixture thereof which comprises reacting the N-mono'alkyl aniline withphthalic anhydride ata tem- N-dialkyl aniline'from the reaction mixture.

6. A process of separating N-monoalkyl and N-dialkyl anilines from amix'turethereof which comprises reacting the N-monoalkyl aniline withphthalic anhydride at a temperature below approximately 140 0., in theabsence of a solvent, distilling un'reactand N-dialkyl anilines from amixture thereof which comprises reacting the-'N-monoalkyl aniline withphthalic anhydride at a temperature below approximately 140 (1,

in the absence of a solvent, distilling unreacted N-dialkyl aniline fromthe reaction mixture, hydrolyzing N-alkyl-phthalanilic acid in theresidue with aqueous caustic alkali to form N-alkyl aniline therefrom,and recovering the latter. r

' 8. A process of separating Nl-methyl and N-dimethyl anilines froma'mixture thereof which comprises reacting the N-methyl aniline withphthalic anhydride at a temperature below approximately 100 0., in theabsence of a solvent, and separating unreacted N-dimethyl aniline fromthe reaction mixture.

which comprises j reacting the N-methyl aniline with phthalic anhydrideat a temperature below approximately 100 C., in'the absence of asolvent, and distilling unreacted 9. A process of separating N-methylandf N-dimethyl anilines from a mixture thereof perature belowapproximately140 in the absence of a solvent,'and distilling unreactedwhich comprises reacting the N-methyl lao anilinewith phthali'canhydrideiat atemperature' below approximately 100 (1., in the absenceof a solvent, distilling unreacted N- dimethyl aniline from thereac'tionmixture under sub-atmospheric pressure, hydrolyzing the residue throughheating the same-with aqueous caustic alkali, and separating N-methyl'aniline from the hydrolysis mixture. 11. A process of separatingNm'ethyl-and N-dimethyl anilines from a--mixture thereof which comprisesreacting the N-methyl aniline with phthalic anhydride in the absence ofa solvent, distilling unreacted N-dimethyl aniline from the reactionmixture, hydrolyzing N-methyl-phthalanilic acid in the residue withaqueous caustic alkali to form N-methyl aniline therefrom, andrecovering the latter.

12. A process of separating N-ethyland N- diethyl anilines from 'amixture thereof which comprises reacting theN-ethyl aniline withphthalic anhydride at a temperature below approximately 140 C., in theabsence of a solvent, and-separating unreacted N-diethyl aniline fromthe reaction mixture,

25 13. A process of separating N-ethyl and N- j H diethyl anilines froma mixture thereof which comprisesfeacting the N-ethyl aniline withphthalic anhydride at a temperature below approximately 140 C.,intheabsence of a 1130 solvent, and distilling .unreacted N-diethylaniline from the reaction mixture. 145A process of separating N-ethylanc N-diethyl'anilines from a mixture thereof which comprises reactingthe Nethyl aniline 9535 with phthalic anhydride ata temperature belowapproximately 140C in theabsence of a: solvent, distilling Vunreacted'N-diethyl aniline from the reaotioncmixture under reduced pressure,hydrolyzing the residue through heating the same with caustic alkali,

and separating N-ethyl aniline from the hydrolysis mixture. 7 7 1 i 15.A process of separatingvN -ethyl and N-diethyl anilines from a mixturethereof T145 which comprises reacting the N-ethyl'aniline with phthalicanhydride in the absence of a solvent, distilling unrea'cted N-diethylaniline from the reaction mixture, hydrolyzing N- ethyl-phthalanilicacid in the residue with aqueous caustic alkali to form N-ethyl anilinetherefrom, and recovering the latter. 16. In a process for separatingN-monoalkyl andN-dialkyl aromatic amines of the benzene series from amixture thereof, the steps which consist in hydrolyzing a N-monoalkylphthalanilic acid through heating the 7 same under super-atmosphericpressure with aqueous caustic alkali, and separating the'N-monoalkylaniline, so liberated, from the hydrolysis mixture. 1 I

" Signed by us this 13th day ofSeptember,

EDGAR C. BRITTON. RAY D. HOLMES. 7

